The present application is the U.S. national stage application of PCT/SE2006/001003, filed Aug. 31, 2006, which claims priority to U.S. Provisional Application No. 60/596,215, filed Sep. 8, 2005.
The present invention relates to a method for automatically registering if a towed vehicle, such as trailer, semi-trailer or the like is connected to a towing vehicle and based thereupon, adjusting gear selection or starting gear selection.
Automatic transmissions of the Automatic Mechanical Transmissions (AMT) type have become increasingly common in heavy-duty vehicles as microcomputer technology has continued to advance and has made it possible, with a control computer and a number of control elements, for example servo motors, to precision-control the engine speed, the connection and disconnection, of an automated clutch between engine and gearbox and coupling members of the gearbox, relative to one another, so that smooth gearshift is always obtained at the correct engine revolutional (rev) speeds. The advantage with this type of automatic transmission compared to a traditional automatic transmission based on a set of planetary gears and with a hydrodynamic torque converter on the input side is firstly that, particularly as regards use in heavy vehicles, it is simpler and more robust and can be produced at substantially lower cost, and secondly that it has higher efficiency, which enhances the prospect for lower fuel consumption.
The automatic mechanical transmissions of the type mentioned above can adjust the selection of the starting gear dependent on the gross weight of the vehicle and road inclination. The gross weight can for example be sensed by measuring the air pressure in an air spring suspension system of a vehicle. The road inclination can be sensed by an inclinometer, which can be for example of the piezoelectric type, as well as other sensor types to achieve the invention herein below disclosed.
When a vehicle is used as a towing vehicle there are several known systems for registering whether a towed vehicle is connected to the towing vehicle or not. The weight of a towed vehicle can have a great effect on the starting performance of the vehicle and, thus, it is important to consider the total gross weight of the towing and the towed vehicles. According to one known technique the signal that indicates that a towed vehicle is connected is used as an input to add an estimated towed vehicle weight to the total gross weight of the towing vehicle and towed vehicle. This signal is often based on sensing some kind of electrical change (current or voltage) in the electrical system of the vehicle, when an electrical system of the towed vehicle is plugged into the vehicle electrical system. In such towed vehicle registering systems there can be registration problems if the towed vehicle for some reason does not have a working electrical system or simply does not have an electrical system.
The total gross weight together with information about road inclination gives an indication of the current vehicle travel resistance. The information about the current vehicle travel resistance is used by a transmission control unit arranged in the vehicle for selecting the right starting gear. The estimated towed vehicle weight is a compromise, which sometimes can give the right starting gear and sometimes a too low start gear ratio which can result in an unsuccessful vehicle take off. The travel resistance of the towed vehicle can depend on how loaded the towed vehicle is or, if it has stood still for a while and has maybe sunken down into muddy ground or possibly the brakes have become rusted thus increasing the travel resistance at start is experienced.
U.S. Pat. No. 6,524,221 discloses a start control device for an automatic transmission, which partly solves mentioned problems. Said device first learns two different starting gears, one for when a trailer is connected and one when no trailer is connected. When the control device is sensing that a trailer is connected it selects the predetermined starting gear with the highest gear ratio, and the opposite when no trailer is connected. Two ways of detecting trailer connected are exemplified; through the brake light connection by sensing some kind of voltage alteration and through an optical sensor in the mechanical connection that connects the vehicle and the trailer.
JP2003-287116 discloses another example of start control device for an automatic transmission capable of determining whether a trailer is being towed or not towed and starting a vehicle according to load conditions. This transmission control device comprises a control means 1 for controlling the gear shift of a multi-stage transmission, a trailer connection detection means 3 for detecting the connection or non-connection of the trailer, a gear position detection means 4, and a gear shift control means 5. The control means 1 selects a proper start gear based on outputs from the trailer connection detection means 3 and output signals from the gear position detection means 4, and controls the gear shift control means 5 so that the vehicle can start at the proper start stage.
It is desirable to present alternative solutions to the problem of registering whether a towed vehicle is connected and to increase the reliability of the automatic system.
In at least one embodiment, an aspect of the invention takes the form of a method for selecting a gear in a vehicle. The vehicle comprises (includes, but is not necessarily limited to) an engine with an engine output shaft connected to an automated mechanical transmission via a clutch; a transmission output shaft connected to at least one driven wheel of the vehicle; means for registering whether a towed vehicle is connected to said vehicle; and at least one control unit for receiving input signals including signals indicative of said towed vehicle connection, and for processing said signals in accordance with programmed logic rules to issue gear selection command output signals to said transmission for gear shifting, where the control unit, when sensing that a towed vehicle has been connected to the vehicle, changes an originally selected first gear to a lower second gear having a higher starting gear ratio compared to said first gear. An aspect of the invention is characterized in that said towed vehicle connection registering means registers at least bounce from when said vehicle bounces into said towed vehicle for connecting the towed vehicle to said vehicle. An advantage of the disclosed method when conducted according to the invention teachings is that a more sure registration of whether a towed vehicle is connected to the vehicle is obtained.
According to one embodiment of the method of an aspect of the invention, said towed vehicle connection registering means comprises a rev speed sensor for sensing rev speed of a shaft rotatably connected to said vehicle wheel, and programmed logic rules in said control unit for registering said bounce in the form of rev speed bounces and determining if a towed vehicle is connected to the towing vehicle.
According to another embodiment of the method of an aspect of the invention, said towed vehicle connection registering means comprises a piezoelectric sensor and programmed logic rules in said control unit for registering said bounce and determining if a towed vehicle is connected to the towing vehicle.
According to another embodiment of the method of an aspect of the invention, the output from an accelerometer is utilized for detecting changes in vehicle acceleration/retardation that are indicative of a towed vehicle being connected and thereby the accelerometer together with appropriate software constitute the “registering means.” Thus, said accelerometer can be used to detect a bounce that typically occurs when the vehicle bounces into the vehicle to be towed.
According to another embodiment of the method of an aspect of the invention, the towed vehicle connection registering means is an air actuated draw coupling for connecting the towed vehicle and includes programmed logic rules in the control unit for registering opening and closing of the draw coupling when the vehicle is being connected to the vehicle.
According to another embodiment of the method of an aspect of the invention, said towed vehicle connection registering means comprises a combination of at least one of: (a) a rev speed sensor; (b) a piezoelectric sensor; (c) an accelerometer, and at least one of: (d) an air actuated draw coupling; (e) an air system pressure sensor; and (f) an electrical characteristic sensor, and programmed logic rules in said control unit for registering changes indicative of a towed vehicle having been interconnected with the towing vehicle. With the use of two or more of the mentioned different ways to register if a towed vehicle is connected the reliability of the system increases.
According to one embodiment of the method of an aspect of the invention, the second gear (when a towed vehicle is connected) is a gear at least two gear steps lower than a gear correspondent to the first gear. At least two gear steps below gives secured vehicle starting performance.
As mentioned above, there can be a problem in registering whether a towed vehicle is connected to the towing vehicle if the towed vehicle for some reason for example does not have a working electrical system or simply does not have an electrical system. Inventive features related to towed vehicle connection registering means as described above solve this problem.